Show revert status chip if revert was created

If a revert of the change was created, determined by scanning the
change messages, then show a "Revert Created" chip next to the
Merged status.
Clicking the chip redirects to the revert created.
The sha of the revert commit is shown in the Change summary section
hidden by default(similar to the Merged As information).

This change does not determine if the revert was submitted or not.
This will be done in a follow up change.

Screenshot: https://imgur.com/a/FZ2adWQ
Change-Id: Ia562e7e09119443f34360d87bf95bb028ccad186

polygerrit-ui/app/constants/constants.ts

diff --git a/polygerrit-ui/app/constants/constants.ts b/polygerrit-ui/app/constants/constants.ts
index be502f7..363f6e5 100644
--- a/polygerrit-ui/app/constants/constants.ts
+++ b/polygerrit-ui/app/constants/constants.ts
@@ -54,6 +54,7 @@
   TAG_SET_ASSIGNEE = 'autogenerated:gerrit:setAssignee',
   TAG_UNSET_ASSIGNEE = 'autogenerated:gerrit:deleteAssignee',
   TAG_MERGED = 'autogenerated:gerrit:merged',
+  TAG_REVERT = 'autogenerated:gerrit:revert',
 }
 
 /**